This invention relates to a method of producing a support or base for a photographic paper, utilizing especially the irradiation by electron beams.
In a conventional support for a photographic paper, which is comprised of a layer coated with a polyolefin resin, the coated layer is formed on the surface of a paper substrate by the use of a die and in a molten state at about 300.degree. C. Therefore, it has drawbacks that the surface of the paper substrate is deformed, the surface quality becomes inferior, and the mirror finishing can be impaired.
Moreover, when the polyolefin resin is applied to form a thin coated layer, it is required for the resin to be applied at a higher temperature, whereby polyolefin itself tends to be pyrolyzed and the layer may yellow and develop pinholes.
Furthermore, while it is preferred for the coated layer to contain a white pigment, the content thereof can not be made large enough when it is dispersed in a molten polyolefin resin, because of low dispersibility of the pigment. Thus the sharpness of photographs becomes insufficient.
In order to eliminate these drawbacks, there has been proposed a method in which a coated layer curable by irradiation with electron beams is formed on a paper substrate and then is allowed to cure by irradiating with the electron beams (Japanese Unexamined Patent Publications Nos. 27257/1982, 30830/1982 and 49946/1982).
According to such a method, the coating and the curing are carried out at a room temperature. Therefore, the surface of the paper substrate is free from the roughness and the development of pinholes. Also, in this method, white pigment is dispersed at a room temperature, and therefore the content of the pigment can be made large enough because of good dispersibility. The sharpness of photographs also can be improved. However, by applying only such irradiation of electron beams as mentioned above, the smoothness of the coated layer can not be sufficient and also desired embossing can not be effected on the surface of the coated layer.
As a way to solve such a problem, there is disclosed in the aforesaid Japanese Unexamined Patent Publication No. 30830/1982 a method in which, the coated layer is pressed against a highly glossy roll under low pressure, is allowed to cure by irradiating electron beams from the rear surface of paper substrate while it is in contact with a form (or emboss) face of the roll, and then is peeled from the form face.
In such a method, however, which is carried out by irradiating the electron beams during contact of the layer with a form member, the coated layer partially remain unpeeled from the surface of the form member, so that the quality is lowered and the productivity becomes inferior. In particular, when concavo-convex embossing is to be effected, it is difficult for such a method to be put into practice because the adherance of coated substance to the form face occurs very frequently.
Moreover, the material capable of curing by irradiation of electron beams is usually adverse to the presence of oxygen and therefore the irradiation is always carried out in an inert gas or the like. Accordingly, the above method requires the roll to be located in an irradiation zone, necessitates a device to be of a large-size, and results in a poor removal rate of oxygen in the irradiation zone. It also results in increased amount of inert gas and poor economic efficiency, and also it sometimes can not achieve sufficient curing.
In the field of printing, there is also known a method in which electron beams are irradiated during contact with a form member to carry out mirror finishing or concavo-convex finishing on the surface of a coated layer (Japanese Unexamined Publications Nos. 164816/1981, 21966/1982, 22204/1982 and 59667/1982). However, the same drawbacks as in the foregoing are inherent to this method.